The present invention refers to an agitator mill or agitator-grinder for the continuous processing of flowable grinding stock.
Agitator-grinders of this type are used for the continuous ultra-fine grinding and/or suspension or disintegrating of liquid, powdery or pulpy substances, as for example food stuffs, dyes, bacterial cultures, etc. Grinding bodies may be beads of glass or ceramics or other hard and wear-resistant materials. Their diameters depend on the degree of reduction desired for the grinding stock to be processed; generally, this width should be of an order of magnitude of from 3 to 0.1 mm (0.1181 to 0.00395 in.).
The smaller the grinding bodies, the smaller must be the width of the separator slit in the separator. Generally, this width should be of an order of magnitude of from 1/2 to 3/4 of the diameter of the grinding bodies. To maintain the very small width of the separating slit required for small grinding bodies within tight tolerances require that the separator ring revolving with the agitator shaft be placed with a high degree of accuracy coaxially with respect to the stationary separator ring and that the axial position of both separator rings with respect to each other be established accurately. This requires that the rotating separator ring be positioned as motion-free as possible in an axial direction.
Another problem inherent in agitator-grinders of the type described is that they cannot be used continuously for the same type of grinding stock generally but that they have to be adjusted more or less frequently for the processing of different grinding stocks. This may require that the grinding chamber and the agitator shaft are exchanged or that frequent changes be made in the separator system either because the separator rings are worn or the width of the separator slit has to be widened or reduced.
In the case of a well-known agitator-grinder of the type described in British Pat. No. 1,325,835, published Aug. 8, 1973, the agitator shaft extends axially through the drive shaft, which for this purpose has been formed tubally. It is braced against the end of the drive shaft which is situated in the discharge chamber by means of two spacers which are placed on the agitator shaft in the region of the separator system and the discharge chamber. The end of the agitator shaft away from the grinding chamber extends beyond the corresponding end of the drive shaft and is attached to it by means of a clamp nut. The rotating separator ring is clamped between the two truncated-con-shaped spacers and through these and the agitator shaft, centered only indirectly with respect to the drive shaft. A change of grinding chamber and agitator shaft necessitates that, after the clamp nut has been loosened, the grinding chamber together with the agitator shaft be moved away from the bearing housing in an axial direction for some distance which is greater than the total length of the drive shaft. The amount of space required for this purpose is considerable and it does not matter whether it is an upright agitator-grinder (with vertical axis) or a long agitator-grinder (with horizontal axis). The difficulties of pulling the grinding chamber and the agitator shaft on the one hand and the bearing housing on the other become especially great when the bearing housing for reasons of design simplicity is attached to a stand or formed in one place and then attached solidly to a foundation.
This well-known agitator as described causes additional difficulties through the fact that the agitator shaft can be removed only together with the rotating separator ring. This requires that it be adjusted with extreme care along the axial direction during reassembling so that the rotating separator ring will again be in an exact axial position with respect to the stationary separator ring.
This is of special importance for separator systems as far as the generally plane, radial separator slit as well as the separator systems with truncated cone-shaped separator slits are concerned. In the case of the letter separator systems as well as those with a cylindrical separator slit any rotational inaccuracy of the rotational shaft caused, for example, by bending stress, and found in the region carrying the rotating separator ring may lead to the undesirable consequence that the width of the circular separator slit may change cyclically and that the rotating separator ring would possibly come into contact with the stationary separator ring. This holds true for noticeable bending in the agitator shaft and a large diameter of the rotating separator ring even if we are concerned with a separator system having a radial separating slit.